Not a duplicate - How can I search for first occurrence of a number less than threshold in a 1D numpy array?

This question was incorrectly marked as a duplicate.

I have an n x 1 numpy array. I want to find the first occurrence of an entry in the array that is less than a threshold.

my code is as follows:

import numpy as np
aa = np.array([4,3,-5,7])


[ 4 3 -5 7]


I expect argmin to return 2 but I'm getting 0. How can I make this work?